The field of the invention is machines for making food products, such as pizzas.
Pizza shells or crust are made from a dough, typically with wheat flour. For large scale production, the dough is prepared in large batches, and individual dough balls are formed. To make a pizza, the dough must first be molded or flattened to the proper shape and thickness. For hand-made pizza, the dough is flattened by pressing it and stretching it, and via the ever popular pizza "toss". Small presses may also be used. For large scale production, a common method for forming pizzas is to press the dough in a pressing machine having one or more dies.
For most pizzas, the pressed pizza dough should preferably produce a finished food product that is close in taste and texture to a hand-made pizza dough. For example, it is preferable that the pressed dough retain its shape after formation. In addition, the pizza should also preferably bake as a hand-made pizza. For instance, it is often preferable that the dough rise during baking, especially in the crust region of the dough, for so called "rising crust" pizza.
Various attempts have been made to produce pizzas having these characteristics. One method uses multiple dies within a press to flatten the pizza dough. The press exerts a large pressing or flattening force on the dough ball. One common design has an inner die plate within a larger outer die ring. Typically, the inner die further includes a groove around its outer edge to form a ridge, or crust, in the pizza dough. The outer die ring very closely surrounds the inner die.
However, this design has a number of disadvantages. To prevent extrusion of pizza dough through the small gap between the inner die plate and the outer die ring, these components must be machined to extremely close tolerances. This increases the cost of production.
Usually, during pressing the dough is also heated by heaters on or around the pizza die. However, the heating of the die causes inner die plate and outer die ring to expand at different rates. This expansion of the components requires additional clearance between the inner die plate and outer die ring, to prevent them from seizing or binding. Unfortunately, the increased clearance also tends to permit dough to extrude through the annular gap between them.
Due to the close fit between the inner die plate and the outer die ring, the non-stick coating, such as TEFLON fluorine-containing polymers, typically used on these surfaces, wears off relatively quickly. This causes the pressed pizza dough to stick to the die, thereby stopping the production line. In practice, removal of the stuck dough from the die generally requires use of makeshift tools, that tend to scratch even more of the non-stick coating off of the die. Once the dough begins to stick, some manufacturers will use higher temperatures and/or longer dwell times to achieve better release characteristics, thereby producing a "hot pressed pizza". However the additional heat produces skin and core temperatures which kill most or all of the yeast in the dough. This prevents the dough from rising when baked.
The very close fit between the inner die plate and outer die ring can cause excessive heating in the outer die ring, even though the heating elements are in contact only with the inner die plate. Often, it is preferable for the pizza dough to rise during baking, e.g., for "rising crust" pizza. If the outer ring gets too hot, the yeast in the dough near the outer ring will be killed, thereby, preventing the crust from rising as desired. The close fit of the inner die plate and outer die ring can prevent the desired thermal isolation of the outer die ring.
For these reasons, the food industry needs better machines and methods for making pizzas, and other food products.